1. Field of the Invention
The present invention relates to linear measurement apparatuses for measuring the dimensions of objects.
2. Description of Prior Art
Conventionally, contact measurement tools, such as tape measures and slide calipers, are used to easily measure the dimensions of objects. However, contact measurement tools may cause deformation of measured objects if the measured objects are deformable, so that measurement errors may be induced. The amount of deformation varies depending on the strength of force applied to the measured object, and it is difficult to compensate for such measurement errors.
Measurement apparatuses with noncontact distance measurement devices such as optical displacement sensors have been used industrially. For example, each of the Japanese Patent Applications JP-9-273912 (published in 1997) and JP 2004-294368 (published in 2004) discloses a thickness measurement apparatus that may be used in production lines of factories. The thickness measurement apparatus includes a pair of spaced optical displacement sensors located along a travel path of sheet materials. Sheet or plate materials are transferred through the gap between the sensors one by one, and each sensor measures the distance between the sensor itself and the material currently moving. On the basis of the measurements by the sensors, the thickness of the material is determined. A similar apparatus is disclosed in http://www.ncsfox.co.jp/product/dn/laser_c.html (Nittetsu Hokkaido Control Systems Co.). However, these conventional noncontact measurement apparatuses have been designed for measuring only objects of uniform thickness with simple contours.